The present invention relates generally to recovery of a data signal. More specifically, sequence detection for encoded transmitted data is disclosed.
FIG. 1 is a block diagram illustrating a typical communication system. Data to be transmitted is scrambled by scrambler 102 and encoded by data encoder 104. The encoded data is transmitted through physical medium 106 and then decoded by decoder 108 and descrambled by descrambler 110.
In general, the physical medium used for transmission is not perfect and thus distorts the transmitted signal. One common impairment is multipath distortion, where the signal travels along different paths and arrives at the receiver at different times. Because of the time delay, different symbols can potentially arrive at the same time and cause intersymbol interference (ISI). Another impairment is the background noise that relates to the receiver front end circuit.
To combat the multipath effect, many systems use a coding scheme to mitigate the detrimental effect. For example, in IEEE 802.11b, a CCK coding scheme is used. Other block codes are used in other systems. The transmitted sequence of symbols is recovered at the receiver by determining a sequence of symbols that best matches the received symbol from a set of possible symbol sequences. When the number of possible symbols is large, as it is for IEEE 802.11b operating at 11 Mbps as described below, the number of combinations of possible symbol sequences to be considered becomes very large for reasonable symbol sequence lengths. As a result, the process of considering possible combinations of symbols becomes complex and time consuming. It would be of great benefit if a better technique could be developed for determining transmitted symbols in a communication system.